Revert "[infra] Roll clang to match the version used by Flutter"

build/toolchain/linux/BUILD.gn

 # Copyright 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/sysroot.gni")
 import("//build/toolchain/ccache.gni")
 import("//build/toolchain/clang.gni")
 import("//build/toolchain/gcc_toolchain.gni")
 import("//build/toolchain/goma.gni")
 
@@ skipping 42 matching lines @@
   ld = cxx
   readelf = "${prefix}readelf"
   nm = "${prefix}nm"
 
   toolchain_cpu = "arm64"
   toolchain_os = "linux"
   is_clang = false
 }
 
 gcc_toolchain("clang_x86") {
-  prefix = rebase_path("//buildtools/toolchain/clang+llvm-x86_64-linux/bin",
+  prefix = rebase_path("//third_party/llvm-build/Release+Asserts/bin",
                        root_build_dir)
   cc = "${compiler_prefix}$prefix/clang"
   cxx = "${compiler_prefix}$prefix/clang++"
   readelf = "readelf"
   nm = "nm"
   ar = "ar"
   ld = cxx
 
   toolchain_cpu = "x86"
   toolchain_os = "linux"
   is_clang = true
 }
 
 gcc_toolchain("x86") {
   cc = "${compiler_prefix}gcc"
   cxx = "${compiler_prefix}g++"
 
   readelf = "readelf"
   nm = "nm"
   ar = "ar"
   ld = cxx
 
   toolchain_cpu = "x86"
   toolchain_os = "linux"
   is_clang = false
 }
 
 gcc_toolchain("clang_x64") {
-  prefix = rebase_path("//buildtools/toolchain/clang+llvm-x86_64-linux/bin",
+  prefix = rebase_path("//third_party/llvm-build/Release+Asserts/bin",
                        root_build_dir)
   cc = "${compiler_prefix}$prefix/clang"
   cxx = "${compiler_prefix}$prefix/clang++"
 
   readelf = "readelf"
   nm = "nm"
   ar = "ar"
   ld = cxx
 
   toolchain_cpu = "x64"
@@ skipping 20 matching lines @@
   cxx = "${compiler_prefix}${toolchain_prefix}g++"
   ar = "${toolchain_prefix}ar"
   ld = cxx
   readelf = "${toolchain_prefix}readelf"
   nm = "${toolchain_prefix}nm"
 
   toolchain_cpu = "${target_cpu}"
   toolchain_os = "linux"
   is_clang = is_clang
 }